An expanding area of technological innovation of diverse application is that of power metallurgy. Metal compositions and forms can be obtained by pressure molding fine metal powders or mixtures of powders into a desired shape. The pressed object may then be heated, in an atmosphere which protects the metal against oxidation, at a temperature at which the crystals of the metal powder grains grow and regrow into each other across the powder grain boundaries without melting. In this fashion, the metallic crystalline equivalent of conventional production by casting and machining is produced. Powder metallurgy methods are especially favorable and desirable where one is concerned with conserving energy and materials as well as avoiding the waste and losses which attend the usual conventional melting, casting, rolling, and machining used to produce metal machinery components.
Requisite to utilization of powder metallurgy is the availability of metal in a suitable degree of fineness, density, and chemical condition. To provide the needs, a wide variety of methods including grinding, atomizing, chemical conversion, and electrodeposition are used.
Electrodeposition is a general method which has the advantage of a wide range of controlling parameters capable of being set at predetermined levels, operable over useful periods with stability and reasonable plant construction costs.
Electrodeposition has been used in the specific context of copper powder production. Commercially available copper powders produced by electrodeposition from water solutions are typically of two general types or classes. One class comprises fine powders of -325 mesh and apparent densities below 1 g/cc. These powders exhibit a fine branched crystal structure suggesting a fern frond and are called dendritic. The other class includes +325 to -100 mesh fine powders with apparent densities usually in a range of 2.5 to 2.7 g/cc. These powders are more compact than the dendritic and are called nodular.
Copper in the usual solid form has a density of 8.9 g/cc, i.e., 1 cubic centimeter of copper in such form weighs 8.9 g. A powder of apparent density of 2.9 requires over 3 cubic centimeters to form 1 cubic centimeter of copper after compression and sintering. Therefore, the greater the apparent density of the starting powder, the smaller the volume that will be required to form the same final product. The powder of highest apparent density obtainable will be most efficient in production of, for example, an extruded heat exchange tube as well as other articles. For a fixed length of extrusion cylinder and expressing ram, in the case of, for example, an extruded heat exchange tube, the longest length will be obtained from the powder of highest apparent density.
In an article entitled "Production of Electrolytic Copper Powder" by F. Wills and E. J. Clugston, Journal of the Electrochemical Society, Vol. 106, pages 362-366 (April, 1959), four general stages of processing were reported during which the properties of the powder, particularly apparent density, could be changed -- (1) electrodeposition; (2) furnacing; (3) grinding and screening; and (4) blending of powders. Most of the grades of powder produced had an apparent density of about 2.7 g/cc or less (Table IV, Page 365). The highest density powder had an apparent density of 3.5-4.0 g/cc. This was powder which had been worked extensively during the first three stages and was reported to have application in specialized usage.
Formation of copper powder by electrodeposition has been examined on a laboratory scale. D. W. Drumiler, R. W. Moulton, and G. L. Putnam, in an article entitled "Electrodeposition of Copper Powder from Acid Sulphate Baths", Industrial & Engineering Chemistry, Vol. 42, pages 2009-2102 (October, 1950), reported experimental results. In some cases, relatively high apparent density in g/ml. were obtained, and the researchers attempted to empirically correlate a number of variables including apparent density. However, the experimental conditions yielded poor efficiency, and the report fails to provide a practical method adaptable to commercial conditions for predictably producing copper powder of high apparent density.
There has been a need in the art for methods of the production of high apparent density copper powder with simplicity and control. The present invention addresses this need and provides for the manufacture of copper powder of high apparent density by electrolytic techniques. Through use of the present invention, high apparent density copper powder can be made with high efficiency, simplicity of operation, and reproduceable control. In addition, the present invention is capable of producing intermediate apparent densities with control and high efficiency in use of material, power and equipment thereby allowing the manufacture of powder having preselected apparent density.
It is therefore a primary object of the present invention to provide a new and improved method of manufacturing high apparent density copper powder.
It is a further object of this invention to provide an electrodeposition method of producing high apparent density copper powder that is relatively simple, reproduceable, and efficient.
Another object of this invention is to provide an electrodeposition method making high apparent density copper powder in which the apparent density of the final product can be readily and predictably controlled.
Yet another object of this invention is to provide a new and improved method of making a high apparent density copper powder starting with a copper powder of relatively low apparent density.
An additional object of this invention is to provide a method of making high apparent density copper powder by an electrodeposition process using low apparent density copper power as a cathode.
Another object of this invention is to provide a new and improved integral process in which a low apparent density copper powder is first produced by an electrodeposition process and then used as a cathode for the production of high apparent density copper powder in a second electrodeposition process.
A further object of this invention is to provide a method of producing high apparent density copper powder from an electrolytic composition by an electrodeposition method without changing the composition of the electrolytic solution during the process.
Additonal objects and advantages of this invention will be set forth in part in the description which follows and in part will be obvious from the description or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the method, compositions, combinations and instrumentalities particularly pointed out in the appended claims.